Abstract : Nucleic acid delivery in vivo via physical means or non-viral vectors still need improvements in particular to reach deep tissues. Sonoporation is highly advantageous for this purpose as ultrasound can be focalised to a particular tissue leading to targeted gene delivery, without alteration of the environing tissues. Few examples of transfection using cationic microbubbles (MBs) and DNA have been reported. We ought to improve the existing systems by developing positively charged MBs able to oscillate in order to follow their fate in vivo and gain in understanding of the pharmacokinetic of the MBs, then target DNA delivery with ultrasound. After optimisation, we obtained MBs in the 1-3 !m range (98% below 10 !m) able to adsorb nucleic acid on their surface. In vitro parameters have been optimised to obtain in vitro transfection both with DNA and siRNA. The systemic injection in mice led to the observation of these MBs in the liver in less than 10 seconds. This investigation allows to address the key parameters to tentatively obtain reproducible gene transfection in vivo.